Incandescible cathode



Aug. l5, 1939. G. HOLST E1' AL 2,159,643

y mcANnEscILE cATHoDE Original Filed Sept. 6, 1934 f/vvf/vrams .5y,awa/410%..

Patented Aug. 15, 1939 TENT GFFCE INCANDE SCIBLE CATHODE Gilles Holstand Hajo Lorens van der Horst, Eindhoven, Netherlands, assignors to N.V.

Philips Netherlands Glceilampenfabrieken,

Eindhoven,

Original application September 6, 1934, Serial No. 743,006. Divided andthis application March 14, 1938, Serial No. 195,890. lin GermanySeptember 7, 1933 6 Claims.

The present invention, which is a division of our copending U. S. patentapplication Serial No. 743,006, now Patent No. 2,119,913 relates toincandescible cathodes, and more particularly to cathodes having thelarge electron-emitting surfaces required for gas-filled dischargetubes, such as rectifying tubes ci large current capacities.

1f such cathodes are to handle large currents they should have a largeelectron-emitting surlo face, and the specific emissivity, i. e. theelectron emission per unit of cathode surface, should be as high aspossible for a given temperature. To obtain a large specific emissivityat a given temperature, the cathode surface is usually activated with asurface layer or coating of a material having a high electronemissivity, for instance a highly-emissive oxide, such as barium oxide.

Various constructions have already been proposed to obtain cathodeshaving a large emitting surface; for instance, according to U. S. PatentNo` 2,052,103 to Mulder et al., a large cathode surface is obtained bywinding into a roll a metallic gauze provided with a highly-emissivecoating. Such construction, however, has certain drawthe wire formingthe gauze. More particularly, the gauze is very readily damaged, andthis is vaggravated by the fact that the wire forming the gauze, insteadof being made of tungsten or other highly refractory metal, is usuallymade of a lower melting-point metal, such as nickel, in order that theoxide layer will more readily adhere thereto. metals the individualwires of the gauze are liable .'-15 to melt, which may impair theoperation of the entire cathode structure. Although the latter drawbackcan be partly removed by providing a plurality of supply wires connectedto various points of the metal-gauze or by Weaving the gauze ofalternately arranged tungsten. and nickel wires, such structures areexpensive and not entirely satisfactory for handling very largecurrents.

According to our present invention, these drawbacks are overcome byproviding a large-surface cathode body, which may be either directlyand/or indirectly heated, in the form oi a composite band which isfolded or wound into a coinpact form. This composite band hasessentially two components, namely, a single continuous elongatedsupport in the form of a metal wire or metal strip which extends theentire length of the band, and a large surface-area member consisting ofa large number of projections which may be individual or be formed as acontinuous membacks which are due especially to the thinness of'k Whenmade of such low melting (Cl. Z50-27.5)

ber; the projections being mechanically and electrically connected withthe support or may be even integral therewith.

Furthermore, in accordance with the invention the projections of thelarge surface-area member extend in a direction substantiallyperpendicular to thesupport, whereby the composite band formsasubstantially flat structure which can ce made in any length in acontinuous operation, and then cut into the desired length and assembledinto a compact assembly, for instance wound into a roll.

The support is given a suicient cross section to act as a supplyconductor for the discharge current, and if desired also for the heatingcurrent without danger of melting, and even if some ci the projectionsshould melt away or break oli, the support remains intact and theoperativeness of the cathode is substantially unaffected.

referably, the support itself is made oi a high melting-point metal, forinstance tungsten, whereas the projecting parts may be formed of a lowermelting-point metal, for instance nickel, to which the oxide rmlyadheres.

More particularly in accordance with the invention, the composite bandis shaped as a comb, in which the support forms the rib or base and theprojecting parts form the teeth. 1f the support is to be made of thesame material as are the projecting teeth, the composite band can beformed by a single stamping. However, we prefer to make the support of agreater thickness and of' a higher melting point metal than that of theteeth.

The composite band may be heated by passing current through the supportand for this purpose the support may be provided with leads which aresealingly carried through the tube envelopes, or, ii also a separateheating element, for instance a lament, is provided, the support endsare electrically connected to the ends of the heating element.

In a preferred embodiment of our invention a composite band according tothe invention is wound into a roll, and this roll is surrounded by ahelically-wound, directly-heated cathode.

With the above-described constructions it is possible to obtain a fiveto tenfold increase of the emitter-carrying surface, which results in anequal increase of the discharge current capacity of the cathode.

In order that the invention may be more clearly understood and readilycarried into eiect, we shall describe the same in more detail withreference to the accompanying drawing, in which:

Figure l is a side view of a comb-shaped coinposite band shown inevolution; and shows the cross-section of the support,

Figure 2 is a comb-shaped band similar to that shown in Fig. 1 buthaving a support and teeth made of a single piece of metal,

Fig. 3 is a top View of a cathode structure employing a cathode bandshown in Fig. l,

Fig. 4 is a partly sectionalized side elevation of a cathode structurecomprising a comb-shaped band as shown in Fig. l, which is surrounded bya directly heated coiled cathode, and

Fig. 5 is a top View, partly in section, of Fig. 4.

The composite band shown in Fig. 1 has the shape of a comb and consistsof a supporting wire or band I carrying laterally extending projecting.teeth 2. The composite band may be formed of a supporting part Ithicker than the teeth 2, and may be made of a refractory metal, astungsten; the projecting teeth 2 being preferably made of nickel towhich an oxide coating, for instance barium oxide, readily adheres.However, support I rnay also be coated with an electron emissive layer.Such a composite band may be formed in any length and then cut to thedesired length.

An alternative construction is shown in Fig. 2 in which the supportingband 3 and the teeth 4 are formed out of one metal strip. This has theadvantage that an excellent mechanical and electrical connection of thesupport and the teeth is obtained.

As shown in Fig. 3, the composite band of Fig. i is rolled into a spiralwhose inner end is secured to a central supporting rod 5 and whoseindiviclual turns are spaced from each other. The spirally woundcomposite band is surrounded by a helically wound heating Wire B, whichis provided with leads 'l and 8 for the supply of the heating current.The outer end of the support I is electrically connected, preferably bywelding, to the supply lead l.

The composite band, preferably including the support I, is coated withan oxide layer and the heating wire 6 is similarly coated. When aheating current is passed through the heating wire 6, one part of thecathode assembly is heated directly and the other part is heatedindirectly., If desired, supporting rod 5 may be electrically connectedto the supply wire 8, in which case the heating current passes throughboth the heating wire 6 and the support I, thus giving a cathodeassembly in which both parts are heated directly as well as indirectly.

For spacing the turns of the composite band, interposed rods, (notshown) may be used, although good results can be obtained when thesuccessive turns of the band are in contact With each other; providedthe apertures and teeth be properly staggered to expose substantiallythe entire cathode to the discharge. Figs. 4 and 5 show the combinationof a cathode structure in accordance with Fig. 1, with a directly heatedcathode 9, the latter forming a coiled lament which surrounds andindirectly heats the composite band cathode body I-2.

The helically wound cathode may also be of a composite structure, and asshown, comprises two tungsten wires IO-IO which are coiled andsurrounded throughout their whole length with a thin helically woundnickel wire I I, the turns of which lie in direct contact with eachother. The unwound end portions of the tungsten wires Iii-I may benickel plated, so that the entire outer surface of the cathode structure9 is provided with a nickel surface. The undulated surface of the nickelwire II is especially favourable for the rm adherence of an oxidecoating. The ends of the tungsten wires IU--IO are welded or otherwiseconnected to lead-in rods I2-I 3, which also serve as supports for thecathode. The supporting strip I of the composite cathode band is weldedat its inner end to the rod which serves as a supply conductor for thedischarge current to the band, which rod is connected at its end to therod I3. The support I may be directly heated in which case the outer endof the support I may be electrically connected to the lead-in rod I2.

Between the large surface body and the cathode 9 tubes I4 of insulatingmaterial (see Fig. 4) for instance of porcelain are provided forspacing, inside of which are disposed metal wires I5 having bent upperend-portions I6 which engage the composite band I-2 and iix the samesecurely within the cathode 9.

The cathode structure shown in Figs. 3 and 4 provides for an emissionwhich, assuming that the same heating energy is used, may be severaltimes the emission which can be obtained by merely using the helicallywound cathode 9.

While we have described our invention in connection with a specicembodiment and in a specific application, we do not wish to be limitedthereto, but desire the appended claims to be construed as broadly aspermissible in view of the prior art.

What we claim is:

1. A compact incandescible cathode body comprising a compositecomb-shaped band having an elongated support for carrying the emissioncurrent, and a large number of straight elongated projecting portionsspaced from each other and extending substantially perpendicularly tothe longitudinal axis of the support, and highly electron-emissivematerial on the surface of said projecting portions, said band beingbent along lines perpendicular to the longitudinal axis of the supportinto a series of convoluted portions forming a compact body providedover its entire cross section with a large number of ducts extendingsubstantially from end to end of the body and allowing access of thedischarge to the interior thereof.

2. A compact incandescible cathode body comprising a metal band havingan elongated supporting portion for carrying the emission current and alarge number of straight elongated portions extending substantiallyperpendicularly to the longitudinal axis of the supporting portion andbeing spaced from each other, and highly electromemissive material onthe surface of -`said extending portions, said band being bent alonglines parallel to the longitudinal axes of said extending portions intoa series of convolutions forming a compact body provided over its entirecross-section with a large number of ducts extending substantially fromend to end of the body and allowing access of the discharge to theinterior thereof.

3. A compact incandescible body comprising a composite band having anelongated support for carrying the emission current and consisting of ahigh-melting-point metal, and a large number of straight elongatedprojecting portions extending substantially perpendicularly to thelongitudinal axis of the support and consisting of a low-melting pointmetal to which electron-emissive materials rmly adhere, and highlyelectronemissive material on the surface of said projecting portions,said band being bentv along lines perpendicular to the longitudinal axis.of the support into a series of convoluted portions forming a compactbody provided over its entire cross section With a large number of ductsextending substantially from end to end .of the Abody and allowingaccess to the interior thereof.

V4. An incandescible cathode body comprising a composite comb-shapedband having an elongated support for carrying the emission current and alarge number of straight elongated projecting portions spaced from eachother and extending substantially perpendicularly to the longitudinalaxis of the support, highly electron-emissive material on the surface ofsaid projecting portions,

said band being bent along lines perpendicular to the longitudinal axisof the support into a series of convoluted portions constituting acompact body provided over its entire cross section with a large numberof ducts extending substantially from end to end of the body andallowing access of the discharge to the interior thereof, and a rod .ofconductive material centrally disposed within the body and electricallyconnected to said support.

5. An incandescible cathode body comprising a composite comb-shapedhandhaving an elongated support for carrying the emission current and alarge number of straight elongated projecting portions spaced from eachother and extending substantially perpendicularly to the longitudinalaxis of the support, said band being bent along lines perpendicular tothe longitudinal axis of the support into a series of convolutedportions constituting a compact body provided over its entire crosssection With a large number of ducts extending substantially from end toend of the body and allowing access of the discharge to the interiorthereof, a -directly-heated helically-Wound cathode surrounding saidbody to heat same tol its proper electron-emitting temperature andhaving a large surface area, and highly electron-emissive material onthe surfaces of said helically-wound cathode and of said projectingportions.

6. An incandescible cathode body comprising a composite comb-shaped bandhaving an elongated support for carrying the emission current and alarge number of straight elongated projecting portions spaced from eachother and extending substantially perpendicularly to the longitudinalaxis of the support, said band being bent along lines perpendicular tothe longitudinal axis of the support into a series .of convolutedportions constituting a compact body provided over its entire crosssection with a large number of ducts extending substantially from end toend of the body and allowing access of the discharge to the interiorthereof, a rod of conductive material centrally disposed Within saidbody and electrically connected to said support, a directly-heatedhelically-Wound cathode surrounding said body to heat same to its properelectron-emissive temperature and having a large surface area, highlyelectron-emissive material on the surfaces of said helically-woundcathode and of said projecting portions, and means supporting said bodyfrom said rod and insulatingly spacing said body from said cathode, saidmeans comprising a plurality of insulating members disposed between saidband and said cathode, and supporting members secured to said insulatingmembers and to said rod.

GILLES HOLST. HAJO LORENS VAN DER HORST.

